1. Field
Example embodiments relate to sensing temperature in semiconductor apparatuses and methods thereof, for example, example embodiments may relate to temperature sensors with self-calibration functions and comparator offsets in response to process variations, and methods thereof.
2. The Conventional Art
Dynamic random access memory (DRAM) devices of volatile memory may need to refresh data in memory cells by themselves in order to preserve data stored in the memory. Due to this self-refresh operation, self-refresh power is consumed in the DRAM devices. It may be important to reduce the self-refresh power in a system requiring low power consumption.
To reduce the self-refresh power, a refresh period may be changed according to temperature, because data holding time may increase with decreasing temperature in a DRAM device. Accordingly, if an area is divided into a plurality of regions for temperature measurements, and a refresh period is increased in a low temperature region, the self-refresh power may be reduced. However, an embedded temperature sensor having low power consumption may be required to detect internal temperature of the DRAM device or any desired portion of the device.
FIG. 1 illustrates a conventional bandgap type temperature sensor. FIG. 2 illustrates a temperature sensing procedure of the conventional bandgap type temperature sensor illustrated in FIG. 1. The temperature sensor illustrated in FIG. 1 is disclosed in Korean Patent Registration No. 10-045736, entitled “Temperature Sensor Having Shifting Temperature Detection Circuit for Use in High Speed Test and Method for Detecting Shifting Temperature”.
Referring to FIG. 1, the conventional bandgap type temperature sensor may include a weighted-resistor string RUA-32RUA for sensing high temperature and a switching unit TU which corresponds to individual resistors of the weighted-resistor string RUA-32RUA. The switching unit TU may selectively short-circuit portions of the weighted-resistor string RUA-32RUA. The switching unit TU may be implemented using transistors, each of which is selectively enabled for short-circuiting in response to a corresponding control signal. The corresponding control signal may be one of signals AU0 through AU5.
Additionally, the conventional bandgap type temperature sensor may include a weighted-resistor string RDA-32RDA for sensing low temperature and a switching unit TD which corresponds to individual resistors of the weighted-resistor string RDA-32RDA. The switching unit TD may selectively short-circuit portions of the weighted-resistor string RDA-32RDA. The switching unit TD may be implemented using transistors, each of which may be selectively enabled for short-circuiting in response to a corresponding control signal. The corresponding control signal may be one of signals /AD0 through /AD5.
A comparator C2 may compare a second voltage V2 with a first voltage V1. V1 may change according to the change in resistance due to the operation of the weighted-resistor string RUA-32RUA or RDA-32RDA, and ON/OFF of each of the transistors in the weighted-resistor string RUA-32RUA or RDA-32RDA. V2 may reflect a voltage of a first diode D1. A comparator C1 may compare the second voltage V2 with a reference voltage Vref of a second diode D2. A comparator C3 may compare an output signal of the comparator C1 with an output signal of the comparator C2. The comparator C3 may output a comparison result signal T45 corresponding to a sensed temperature.
The temperature sensor illustrated in FIG. 1 normally operates only in response to a trip point at a particular temperature. However, because the temperature sensor illustrated in FIG. 1 is very sensitive to variation in manufacturing processes, temperature tuning may need to be performed in individual chips at a wafer level in order to adjust a trip point to a designed or desired temperature point. It may be necessary to detect a shift temperature caused by the variation in manufacturing processes in order to perform temperature trimming during the temperature tuning. In addition, it may be necessary to perform tests at high temperature and low temperature in order to measure an error in weighted resistance caused by process variations.
Referring to FIG. 2, a shift temperature is 5° C., and may correspond to a difference between a designed temperature point (e.g., a target temperature of 45° C.) and a trip point before trimming (e.g., an untrimmed temperature of 50° C.). Temperature sensing may be performed at a high test temperature Tc of 85° C. in order to measure the shift temperature. Initial settings may be: AU5, AU4, AU3, AU2, AU1, AU0=0, 0, 0, 0, 0, 0. Subsequently, if “1” is applied to the control signal AU5 corresponding to a most significant bit (MSB), temperature may increase by 32° C. from a current trip point as illustrated by the arrow ARU5a. Because the increased temperature, i.e., 50° C.+32° C. is lower than the test temperature of 85° C., the control signal AU5 has a value of “1” and the entire digital signal becomes (1,0,0,0,0,0).
If “1” is applied to the control signal AU4, temperature may increase by 16° C. from the current temperature of 82° C. as illustrated by an arrow ARU4a. Because the increased temperature, i.e., 82° C.+16° C. is higher than the test temperature of 85° C., the control signal AU4 has a value of “0”. Therefore, a previous start point of 82° C. may become the current start point; and the entire digital signal remains (1,0,0,0,0,0).
If “1” is applied to the control signal AU3, temperature may increase by 8° C. from the current start point of 82° C. as illustrated by the arrow ARU3a. Because the increased temperature, i.e., 82° C.+8° C. is higher than the test temperature of 85° C., the control signal AU3 has a value of “0”. Therefore, the previous start point of 82° C. becomes the current start point; and the entire digital signal remains (1,0,0,0,0,0).
If “1” is applied to the control signal AU2, temperature may increase by 4° C. from the current start point of 82° C. as illustrated by the arrow ARU2a. Because the increased temperature, i.e., 82° C.+4° C. is higher than the test temperature of 85° C., the control signal AU2 has a value of “0”. Therefore, the previous start point of 82° C. becomes the current start point; and the entire digital signal remains (1,0,0,0,0,0).
If “1” is applied to the control signal AU1, temperature may increase by 2° C. from the current start point of 82° C. as illustrated by the arrow ARU1a. Because the increased temperature, i.e., 82° C.+2° C. is lower than the test temperature of 85° C., the control signal AU1 has a value of “1”. Therefore, a temperature of 84° C. becomes the current start point; and the entire digital signal becomes (1,0,0,0,1,0).
If “1” is applied to the control signal AU0, temperature increases by 1° C. from the current start point of 84° C. as illustrated by the arrow ARU0a. Because the increased temperature, i.e., 84° C.+1° C. is equal to the test temperature of 85° C., the control signal AU0 has a value of “1” and the entire digital signal becomes (1,0,0,0,1,1).
Accordingly, the digital signal becomes (1,0,0,0,1,1). Because the digital signal (1,0,0,0,1,1) is equal to a decimal value of 35, if 35° C. is subtracted from the test temperature of 85° C., the current trip point is detected as 50° C. Accordingly, the temperature sensor illustrated in FIG. 1 normally operates only when the current trip point of 50° C. is trimmed to the target temperature of 45° C.
Arrows ARU5 through ARU0 indicate the increase in temperature due to resistance error. Referring to FIG. 2, temperature increase due to actual resistance, (e.g., ARU5) is less than temperature increase due to ideal resistance (e.g., ARU5a). A result of sensing performed at ideal resistance and at the high test temperature of 85° C. is (1,0,0,0,1,1). However, a result of sensing at actual resistance and at the high test temperature of 85° C. is (1,0,0,1,1,1), as illustrated in FIG. 2. Accordingly, error in the actual resistance may need to be obtained in order to accurately sense temperature. It is may be necessary to perform a test at the high test temperature Tc of 85° C. and a test at a low test temperature Td of −5° C. in order to obtain the resistance error. Sensing (illustrated by arrows ARD5 through ARD0) performed at the low test temperature Td of −5° C. is similar to the sensing performed at the high test temperature Tc of 85° C. If a value obtained by subtracting the low test temperature Td of −5° C. from the high test temperature Tc of 85° C. (i.e., 85−(−5)=90) is divided by a value obtained by adding the sensing result of 100111 (=39) at the high test temperature Tc of 85° C. to a sensing result of 111101 (=61) at the low test temperature Td of −5° C. (i.e., 39+61=100), a resistance error of about 10% (i.e., 90/100=0.9) is calculated.
As described above, with respect to the conventional bandgap type temperature sensor, tests need to be performed at two or more temperatures in order to measure an error; and temperature sensing resolution is decreased due to offsets among the three analog comparators. Moreover, temperature trimming must be performed for normal temperature sensing. Since only information on whether a measured temperature is higher or lower than a target temperature can be obtained, a plurality of weighted-resistor strings and switching units are required to sense various temperatures. Furthermore, resistance of a weighted-resistor string becomes double per bit to improve resolution, and therefore, the increase in a circuit area results in the increase in manufacturing cost. In addition, accuracy is decreased due to nonlinearity between voltage and temperature in a diode.